China, euro zone sovereign debt and the potential fallout from Brexit top the escalating list of concerns for the Bank of England (BOE), according to a report published on Wednesday which warns that risks to global stability have spiked in the past six months.

The U.K.'s central bank's semi-annual Financial Stability Report states, "Vulnerabilities stemming from the global environment and financial markets, which were already elevated, have increased further since July."

Red flag over China

Chris Ratcliffe | Bloomberg | Getty Images

China's burgeoning debt levels and rapid rate of credit expansion are singled out as significant red flags, with the report noting a 100 percentage point spike in the country's non-financial sector debt relative to gross domestic product (GDP) since the 2008 financial crisis. The ratio currently stands at around 260 percent of GDP.

"This is extraordinary leverage for an advanced, let alone, an emerging economy," the BOE Governor Mark Carney said at a press conference to launch the report.

The "near-record" pace of net capital outflows from China during the third quarter and a 3 percent depreciation in the Chinese renminbi against the U.S. dollar since the publication of the BOE's July report were also highlighted as reasons for concern.

Euro area dynamics

Turning to nearer neighbors, the governor broke down the key risks emanating from some euro area economies into, firstly, existing sovereign debt dynamics and, secondly, threats to the resilience of parts of the trading bloc's banking system.

Carney noted the vulnerability of elevated sovereign debt levels to a leap in borrowing costs or diminished growth prospects on the back of either trade or political headwinds.

Moving even closer to home, the governor raised the looming specter of the U.K.'s impending departure from the European Union (EU), noting banks located domestically currently supply over half of the debt and equity issuance from continental firms and account for over 75 percent of foreign exchange and derivatives activity in the U.K.

Consequent fears of contagion were emphasized by Carney as he discussed the risk of a disruption in services provided to the European real economy spilling over to hit the U.K. economy through trade and financial links.

While clearly stating that the largest risks to U.K.financial stability are global in nature, the governor went on to acknowledge that a lack of clarity over how Brexit will unfold means many unknowns cloud the current outlook.

"It will take time to clarify the U.K.'s new relationships with the EU and the rest of the world. And the orderliness of the U.K. economy's adjustment to these changes will influence the risks to financial stability," Carney said.